130,761 research outputs found
Aspect-ratio dependence of the transition to the ultimate state of turbulent Rayleigh-Bénard convection
No full textWe report on measurements of the ultimate-state transition in turbulent Rayleigh-B\'enard convection obtained in a large facility known as the ``Uboot of G\"ottingen" and using pressurized sulfur hexafluoride as the convecting fluid. We found that the transition occurs over a range of which becomes more narrow as increases, ranging from which is at most weakly dependent on and close to to which varies from about for to about for
The Göttingen rotating turbulent Rayleigh-Bénard convection facility
No full textThermally driven turbulent convection under the influence of global rotation is ubiquitous in nature. Well known examples are the outer convective shell of our Sun and the outer liquid core of the Earth. Trying to understand the underlying dynamics of such flows is highly challenging, not only because of the enormous range in length- and time-scales that are involved with these geo/astrophysical cases and the complex interaction of hydrodynamics with electromagnetism, but also because direct measurements on these systems are most often impossible to carry out. We gain access to direct measurements by isolating part of the problem: We focus solely on the hydrodynamical aspects of turbulent convection by performing experiments in the lab and making comparisons with direct numerical simulations (DNS). The canonical system that we use to study such flows is Rayleigh-B\'enard convection (RBC), the flow between a warm bottom plate and cold top plate, in a fluid-filled upright cylindrical cell that is rotating around its geometrical axis. This presentation will focus on the newly constructed rotating RBC facility at the Max Planck Institute for Dynamics and Self-Organization (MPIDS) in G\"ottingen
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Direct Numerical Simulation of Turbulent Convection in a Rectangular Rayleigh-Benard Cell
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Rayleigh-B\'enard convective motion of stratified fluids in the Earth's troposphere
No full textRecently, Kaladze and Misra [Phys. Scr. 99 (2024) 085013] showed that the
tropospheric stratified fluid flows may be unstable by the effects of the
negative temperature gradient and the temperature-dependent density
inhomogeneity arising from the thermal expansion. They also predicted that the
modification in the Brunt-V\"ais\"al\"a frequency by the density inhomogeneity
can lead to Rayleigh-B\'enard convective instability in the tropospheric
unbounded layers. The purpose of the present work is to revisit the
Rayleigh-B\'enard convective instability in more detail by considering both
unbounded and bounded tropospheric layers. We show that the conditions for
instability in these two cases significantly differ. The critical values of the
Raleigh numbers and the expressions for the instability growth rates of thermal
waves in the two cases are obtained and analyzed. In the case of the bounded
region, we also derive the necessary boundary conditions and note that the
vertical wave number is quantified, and the corresponding eigenvalue problem is
well-set.Comment: 10 pages, 5 figure
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dynamics of large-scale structures and heat transfer in turbulent mixed convection
No full textLow frequency oscillations have been observed in the heat transfer of mixed convection in a rectangular cavity with an aspect ratio of and .~Mixed convective flow at , , and has been studied to determine the nature of these oscillations. Therefore Particle Image Velocimetry (PIV) and temperature measurements have been performed under ambient and high pressure conditions. The PIV results have been analysed using Proper Orthogonal Decomposion (POD) to identify the characteristic frequencies of the coherent large-scale structures and their dynamics have been compared with the low frequency oscillations found in the heat transfer
Evaporating Rayleigh-B\'enard convection: prediction of interface temperature and global heat transfer modulation
No full textWe propose an analytical model to estimate the interface temperature
and the Nusselt number for an evaporating two-layer
Rayleigh-B\'enard configuration in statistically stationary conditions. The
model is based on three assumptions: (i) the Oberbeck-Boussinesq approximation
can be applied to the liquid phase, while the gas thermophysical properties are
generic functions of thermodynamic pressure, local temperature, and vapour
composition, (ii) the Grossmann-Lohse theory for thermal convection can be
applied to the liquid and gas layers separately, (iii) the vapour content in
the gas can be taken as the mean value at the gas-liquid interface. We validate
this setting using direct numerical simulations (DNS) in a parameter space
composed of the Rayleigh number () and the temperature
differential (), which modulates the variation of
state variables in the gas layer. To better disentangle the variable property
effects on and , simulations are performed in two
conditions. First, we consider the case of uniform gas properties except for
the gas density and gas-liquid diffusion coefficient. Second, we include the
variation of specific heat capacity, dynamic viscosity, and thermal
conductivity using realistic equations of state. Irrespective of the employed
setting, the proposed model agrees very well with the numerical simulations
over the entire range of investigated
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